Twitpic

If you post a photo on the Web, it still belongs to you, right? Well, be sure to read the fine print.

World Entertainment News Network, a news and photo agency, announced this month that it had become the “exclusive photo agency partner” of Twitpic, a service with over 20 million registered users that allows people to upload images and link to them on Twitter. The deal allows the agency to sell images posted on Twitpic for publication, and to pursue legal action against those who use such images commercially without its permission, according to the agency.

“There has been much unauthorized use of Twitpic images which we shall be addressing without delay,” said Lloyd Beiny, the agency’s chief executive.

World Entertainment News, whose photo business revolves largely around shots of celebrities, says it is interested only in the photographs posted to the accounts of people like Britney Spears, Russell Brand and Demi Moore. But the scope of the deal is not clear, and professional photographers are worried that it could allow the agency to profit from any photo posted to Twitpic. Others say Twitpic’s move shows the tenuous control people have over what they post through Internet services.

The extent of that control is typically laid out in the terms of service that users agree to when they sign up for Internet services and smartphone applications. But the more such services people use, the harder it becomes to keep track of the things to which they are agreeing. And of course many terms of service, which are heavy on legal language, include clauses that assert the company’s right to change them without notice.